In that area of data processing concerned with data storage, magnetic disc products have become increasingly important. This is due to random access to data and a wide variety of storage capacities, access times and other features for tailoring to specific applications. For example, a module or group of fixed discs in a single drive can have a storage capacity of up to 400 megabytes. On the other hand, a drive utilizing a single flexible disc may have a capacity of from 1/2 to 2 megabytes, and of course, costs less.
The flexible disc is made of a non-magnetic material, for example a polyethylene or polyester. It is typically 0.003 inches (0.08 mm) thick, and can have a diameter of 8 inches (20.5 cm) or 5 inches (13 cm). At its center is a circular drive hole. For storage of data, each disc recording surface is provided with series of concentric tracks between the drive hole and the disc outer edge, usually at a density of 48 tracks per inch, or approximately 0.53 mm apart from one another.
Flexible and not self-supporting, the disc is permanently enclosed in a jacket of plastic or stiff paper. The jacket has at least two openings; a circular opening at the center corresponding to the drive hole of the disc, and an elongated slot directed radially of the disc through which a read/record heads have access to the disc recording surface.
A disc drive apparatus is used for writing and reading data. The drive includes a housing in which the disc is enclosed, and structure for rotating the disc relative to the housing, e.g., a rotatable spindle, a cone or collet for clamping the disc to the spindle and a motor for rotating the spindle and cone. The drive further includes a carriage movable radially of the disc. Mounted pivotally on the carriage is a swing arm, or--in connection with a two-sided flexible disc--two opposed swing arms. A gimbal spring is mounted in cantilever fashion with respect to each swing arm, and carries at its free end a read/record head. Each gimbal spring has a dimple or up-raised portion centered on its associated head. A stiffener, attached to the gimbal spring, contacts the dimple and urges the head against its associated recording surface whenever the swing arms are in their load position. A desired location on the disc surface is reached by selecting the disc angular position and carriage radial position corresponding to such location.
The gimbal spring is designed to give the head nearly instantaneous pitch and roll capability to follow any irregularities in the disc recording surface. The stiffener and dimple provide a pivot point about which the head can pitch and roll. The combination of stiffener and dimple is shown in U.S. Pat. No. 3,896,495 to Beecroft granted July 22, 1975, and in U.S. Pat. No. 4,089,029 to Castrodale et al granted May 9, 1978. As is taught in the Beecroft reference, the selection of materials and design of the gimbal spring can enhance the rapid pitch and roll capability, principally by minimizing the spring constant of the gimbal, i.e., the force required per unit length of elastic spring deflection.
Yet another requirement of the gimbal spring, however, is its ability to support the read/record head in a controlled attitude, particularly when the head is not held against the disc recording surface. The importance of stability when the head is removed from the disc is that if a head is free to dangle near the disc, its edges can strike the recording surface, damaging the head, the disc surface or both and causing loss of data.
The need for head stability is recognized in the Castrodale reference, which shows a pair of fingers integral with the stiffener. In the reading and recording (loaded) position, these fingers are free of the gimbal spring. As the head is retracted, the stiffener is removed from the dimple and subsequently the fingers engage the gimbal to stabilize the head. In head loading, the fingers are disengaged from the gimbal prior to stiffener-dimple contact. Head loading and retraction thus involve brief spans of time during which neither the fingers nor the stiffener contacts the gimbal spring, and the spring alone supports the head. Consequently, to avoid head and disc injury, the gimbal spring must be sufficiently rigid to control head attitude. Yet increased stiffness reduces the head's capability to follow disc undulations and surface irregularities. Another problem, which occurs at each loading, is the shock to the head caused by impact of the stiffener against the dimple. The resulting vibrations can cause damage and reduce head life.
It is an object of this invention to positively control the head attitude in order to eliminate the possibility of damage to the head or disc recording surface. A further object of the invention is to accomplish head attitude control independently of the gimbal spring stiffener. Yet another object is to eliminate the shock caused by stiffener impact against the dimple.